DE1274420B - Corrosion inhibitor for steels - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN MIW PATENT OFFICE Int. α .:

C23f

EDITORIAL

German class: 48 dl -11/06

Number: 1274420

File number: P 12 74 420.6-45 (B 65733)

Filing date: January 31, 1962

Open date: August 1, 1968

The invention relates to the prevention of corrosion of steel by aqueous potassium carbonate solutions, when the solutions are used as a washing medium to remove carbon dioxide and hydrogen sulfide can be used from gas mixtures and come into contact with steel surfaces in the process.

For several years, potassium carbonate solutions have been used extensively to remove carbon dioxide and hydrogen sulfide from industrial gas mixtures, e.g. B. from gas mixtures that occur in the partial oxidation of gaseous, liquid or solid fuels or in the reaction of carbon oxide with water vapor for the purpose of generating hydrogen, or from naturally occurring gaseous hydrocarbons, which often contain large amounts of _{CO 2} and H _{a S} are contaminated at the same time. The use of potassium carbonate solutions for this purpose is described in detail in German Auslegeschrift 1,084,425 and German Patent 1,133,495, for example. During this washing process, CO ₂ and H ₂ S are absorbed by the aqueous potassium carbonate solution and converted into potassium bicarbonate or potassium bisulfide by reaction with the solution. The solution circulates continuously between an absorption tower, in which CO ₂ and H ₂ S are absorbed, and a regeneration tower, in which they are desorbed by countercurrent boiling of the solution and stripping with steam.

Since large amounts of gas are treated in large-scale processes, they are necessary for scrubbing Plants correspondingly extensive. The absorption and regeneration towers in a typical industrial plants can, for example, have a height of 18 m and a diameter of 2.5 m. For this reason it is of course very important from an economic point of view that they be relatively cheap Materials such as low carbon steel used to build the equipment and relatively expensive alloys, such as corrosion-resistant steel, inconel and the like, should be avoided as far as possible.

It has been found, however, that ordinary mild steel as well as many steel alloys are corroded by the aqueous potassium carbonate solutions used in the above processes. In a solution to which no anti-corrosive agent has been added, the rate of corrosion is usually highest when the contaminant to be removed consists of carbon dioxide alone. If the impurity to be removed consists of H ₂ S alone or a mixture of H ₂ S with CO ₂ , which contain a fairly high _{proportion of H 2} S, the corrosion inhibitor for steels is

Applicant:

Benson, Field & Epes, Malvern, Pa. (V. St. A.)

Representative:

Dr.-Ing. A. v. Kreisler, Dr.-Ing. K. Schönwald,

Dr.-Ing. Th. Meyer

and Dr. J. F. Fues, patent attorneys,

5000 Cologne 1, Deichmannhaus

Named as inventor:
Joseph Herman Field,
Daniel Bienstock, Pittsburgh, Pa. (V. St. A.)

Claimed priority:
V. St. v. America December 1, 1961
(157 053)

speed is very low and in many cases no anti-corrosion agent is required. This is usually the case when less than 9 moles of CO ₂ are _{encountered in 1 mole of H 2 S.} Obviously, H ₂ S proportions at this level effectively passivate the steel surfaces and thereby reduce the corrosion rate to acceptably low values even without the addition of an anti-corrosion agent. However, if the impurity consists mainly of CO ₂ in a mixture with smaller _{amounts of H 2} S, ie if less than 1 mole of H ₂ S meets 9 moles of CO ₂ or, in other words, if the gas mixture contains at least 9 _{moles of H 2 S} Contains moles of CO ₂ , the passivating effect of these small _{amounts of H 2} S is generally insufficient to reduce the rate of corrosion to a tolerable level.

In the former case, ie when removing CO ₂ alone, the corrosive effect of the solution on steel can be reduced by adding various anti-corrosion agents, e.g. B. small amounts of potassium dichromate or other dichromates, to a tolerable level

809 588/409

3 4

be weakened. Under these conditions, therefore, the use of metavanadate salts as the dichromate remains in solution and remains effective for a long time as an inhibitor in an aqueous potassium carbonate solution. In the presence of H ₂ S, however, when removing carbon dioxide and / or dichromates and many other anti-corrosion agents, hydrogen sulfide from gas mixtures is used, e.g. B. nitrites, the disadvantage that they quickly lose their anti-corrosive 5 to prevent corrosion of the steel surfaces and often come into contact with the solution, an undesirable insoluble residue in the Suitable is any metavanadate that at least

Leave a solution. Frequently the presence of 0.05 percent by weight in aqueous potassium carbonate of trace amounts of H ₂ S, e.g. B. 10 to 100 parts per solution is soluble. Alkali million are preferably in the gas to be treated in order to bring the ver io metavanadate, in particular sodium metavanadate, consumption of the corrosion protection potassium metavanadate or ammonium metavanadate used to date to an uneconomical level. used. If necessary, the metavanadate is missing an inhibitor that is formed in the presence of in situ, for example by direct aqueous potassium carbonate solutions in which both the addition of vanadium pentoxide to the potassium carbonate H ₂ S and CO _{2 are} adsorbed, remains stable and 15 solution, Potassium metavanate effectively protects against corrosion from these solutions by reacting with steel. In particular, there is no such inhibitor for The metavanadates are even in small amounts

the treatment of CO ₂ and H ₂ S containing effectively. They can be used in concentrations of only gas mixtures in which the H ₂ S amount is in the range 0.01%, based on the total weight of the solution, from traces to amounts that have a molar ratio of 20. Corresponding to concentrations above about 2 Ge-H ₂ S: CO ₂ of about 1: 9. As the percentages by weight usually do not result in an increased already mentioned, the known corrosion effectiveness can, but usually does not damage either. Protective agents in this range their effectiveness are preferred, concentrations are usually two, and the passivating effect of see 0.05 and 0.5 percent by weight, at which maxi-H ₂ S is not sufficient to make the corrosion rate 25 times effectiveness and economy achieved to a tolerable level Lower level. The problem is becoming.

especially acute when the molar ratio H ₂ S: CO ₂ Even with highly concentrated solutions that contain two

ranges from about 1:20 to 1: 1000. Mixtures, for example 40 percent by weight of potassium carbonate of this type, are often found with the partial oxy- gen and at their boiling point or in its vicinity dation of carbon-containing fuels, which are used, reduce the metavanadates contain relatively small amounts of sulfur, extremely effective in reducing the rate of corrosion. For example, a typical gas mixture of steel surfaces can be negligible. The metavanadates protect the partial oxidation of a sulfur-containing crude oil in systems such as those described in the or a sulfur-containing coal 5 to 35 volume German Auslegeschrift 1 084 425, percent CO ₂ and 0.01 to 0.5 volume percent H ₂ S 35 being usually contain about 20 to 40 percent by weight. Aqueous solutions containing K ₂ CO _{3 at temperature}

It has now been found that Metavanadatsalze, the doors may be used from about 100 to 140 ⁰ C, in in aqueous potassium carbonate solutions at least to a large extent the existing made of steel and are soluble to the small extent, not only very effective solution in contact apparatuses and The corrosion of steel by these solutions at 40 allow the use of low carbon gas scrubbing processes to reduce, but rather steel or relatively cheap alloy steels that they also have the extremely important advantage for most parts of the plant. Also high-alloyed that their solubility and corrosion-inhibiting steels, z. B. chromium-nickel steels, give the salts effect in the presence of co-existing. increased corrosion resistance, but make their CO ₂ and H ₂ S preserve. Because of their overuse unnecessary, except in individual places the surprising ability to withstand the reduction and thus the systems that are particularly exposed to attack, precipitation by H ₂ S. B. for pump wheels.

the metavanadate salts are a solution of the above.

problems outlined, ie, they grant effective lent the excellent corrosion protection, the corrosion protection in such critical areas, 5 ° steel surfaces are granted, which are concentrated with a concentrated in which small _{amounts of H 2} S mixed with aqueous potassium carbonate solution in the presence of considerable CO ₂ - Quantities occur. Under these CO ₂ alone and from CO ₂ -H ₂ S mixtures in conditions under which the previously used stirring comes. The tests were carried out to prevent corrosion inhibitors by reacting them with a 40% aqueous potassium carbonate-hydrogen sulfide solution containing CO ₂ or a CO ₂ -H ₂ S mixture to reduce the effectiveness of the metavanadate salts and to reduce the rate of corrosion by bubbling the gas through the solution from steel to saturated, while those of negligible values at their boiling point. The metavanadate salts pointing 109 ⁰ C was kept. The CO ₂ -H ₂ S mixture had the additional advantage that it consisted of 99.7 volume percent CO ₂ and 0.3 volume of the CO ₂ absorption in the absorption column about 60 percent H ₂ S. In the solution were polished disks tend to increase so that some reduction in low carbon steel is possible for the absorption tower size in the table. mentioned periods. In a series of experiments

The use of metavanadate salts as inhibitors was already known, although a small amount of sodium metavanadate in the treatment of steels with H ₂ SO ₄ is also already known in the table, but 65 is not readily added from this. In the other series of experiments it was not possible to deduce that metavanadate also uses the inhibitor. The rate of corrosion Corrosion of steels by alkaline solutions was measured as weight loss after removal of the ability to prevent. The invention relates to corrosion products from those exposed to the solution

I 274

Place the discs determined. The experiments had the following results:

at
game Type of K ₂ CO ₃ solution temperature
⁰ C Inhibitor concentration
in percent by weight,
based
on total solution Attempt
duration
Days Corrosive
swiftly
speed
cm / year 1
2 saturated with CO ₂ 40 ° / ₀ cent K ₂ CO ₃ solution
40% K ₂ CO ₃ -LoSMIg with 99.7% CO ₂ + 0.3%
H ₂ S 109
109
109
109
109
109
109 0.2% NaVO ₃
0.1% NaVO ₃
0.2% NaVO ₃
0.2% K ₂ Cr ₂ O ₇
0.2% K ₂ Cr ₂ O ₇ 14th
30th
30th
30th
30th
30th
31 0.864
0.0254
0.00015
0.000102
0.000102
0.000076
0.0254 3
4th
5
6th
7th 40% K ₂ CO ₃ solution saturated with CO ₂
40% K ₂ CO ₃ solution saturated with CO ₂
40% K ₂ CO ₃ solution, saturated with a
Mixture of 99.7% CO ₂ + 0.3% H ₂ S ....
40% K ₂ CO ₃ solution saturated with CO ₂
40% ig ^e K ₂ CO ₃ solution, saturated with a
Mixture of 99.7% CO ₂ + 0.3% H ₂ S ....

It can be seen from the above values that the metavanadate is extremely effective in reducing _{the rate of corrosion in the presence of both pure CO 2} and CO ₂ -H _{2 S mixtures.} It can be seen that despite a certain reduction in the rate of corrosion due to the presence of the small amount of H ₂ S in the solution according to Example 2, which contained no anti-corrosion agent (due to the low passivating effect of the H ₂ S), the rate of corrosion was 0.0254 cm / year is still too high. In Example 5, the metavanadate provided the necessary protection and reduced the rate of corrosion to one hundredth. K ₂ Cr ₂ O ₇ was effective in example 6 in the presence of pure CO ₂ , but the dichromate in example 7 _{quickly formed a dark precipitate in the presence of H 2} S and completely lost its corrosion-inhibiting effect. The rate of corrosion in this case was the same as that of the solution according to Example 2, which did not contain any anti-corrosion agent.

In a typical application of the method described in German Auslegeschrift 1084 425, a 30% aqueous K ₂ CO ₃ solution was used to remove CO ₂ and H ₂ S from a gas mixture that was produced by partial oxidation of a sulfur-containing Middle Eastern crude oil and then Water gas reaction had been established and had the following approximate composition: 3% CO, 64% H ₂ , 32% CO ₂ , 0.5% H ₂ S and about 0.5% CH ₄ + N ₂ . The absorption and regeneration towers and most of the piping were made of low carbon steel. The maximum temperatures of the solution amounted to 118 ⁰ C in the absorption tower and 113 ° C in the regeneration tower. By adding 0.2 percent by weight of NaVO ₃ to the K ₂ CO ₃ solution, the rate of corrosion of the mild steel surfaces was kept at values below 0.0127 mm / year. Only small additions of NaVO ₃ , which were necessary to supplement the normal loss of solution, were required to maintain the original concentration of 0.2%. In contrast, the rate of corrosion in such a system without the addition of an anti-corrosion agent is over 0.25 mm / year, so that more frequent replacement of pipelines and other parts of the washing system is necessary. Potassium dichromate and various other anti-corrosion agents were ineffective, apparently due to rapid consumption due to reaction with the H ₂ S present in the raw gas.

Claims (5)

Patent claims: 1. Use of metavanadate salts as an inhibitor in an aqueous potassium carbonate solution, used in the removal of carbon dioxide and / or hydrogen sulfide from gas mixtures is used to prevent corrosion of the steel surfaces that come into contact with the solution come. 2. Use of the inhibitor according to claim 1 in amounts of 0.01 to 2 percent by weight, preferably 0.05 to 0.5 percent by weight, based on the solution. 3. Use of the inhibitor according to claim 1 and 2 in the form of potassium, sodium or Ammonium metavanadate. 4. Use of potassium metavanadate as an inhibitor in an aqueous potassium carbonate solution according to claim 1 to 3, which is formed in situ by adding vanadium pentoxide to the solution will. 5. Use of the inhibitor according to claim 1 to 4 in the treatment of gas mixtures to 1 mole of H ₂ S at least 9 moles of CO _2, preferably 1 mole to 1000 moles H CO ₂ containing ₂ S about 20 microns. Considered publications:
U.S. Patent No. 2172,353;
Otto Vogel, "Handbuch der Metallbeizerei", Vol. II, 1951, p. 457. 809 588/409 7.68 © Bundesdruckerei Berlin